Aluminium alloy for use as core material in brazing sheet

ABSTRACT

An aluminium alloy for use as a core material in brazing sheet, comprising, in weight %: Mn 0.7-1.5, Cu 0.6-1.0, Fe not more than 0.4, Si less than 0.1, Mg 0.05-0.8, Ti 0.02-0.3, Cr 0.1-0.25, Zr 0.1-0.2, balance Al and unavoidable impurities, wherein 0.20&lt;(Cr+Zr)≦0.4, the alloy being capable of obtaining in the post-brazing state 0.2% yield strength of at least 65 MPa and having a corrosion life of more than 11 days in a SWAAT test without perforations in accordance with ASTM G-85.

FIELD OF THE INVENTION

This invention relates to an aluminium alloy for use as a core materialin brazing sheet, to a brazing sheet comprising the aluminium alloy ascore material, to the use of the aluminium alloy as core material of abrazing sheet in a brazed assembly and to a brazed assembly containingat least one member having the aluminium alloy as core material. Thealuminium alloy is of the AA3xxx type. The invention has the particularadvantage that the alloy is non-heat-treatable, i.e. it does not requirepost-brazing ageing treatment. A principle use of brazing sheetcontaining such alloy is in heat exchangers, such as vehicle radiators,in which water is one heat-exchanging medium. Herein the term sheetmaterial includes tube material.

DESCRIPTION OF THE PRIOR ART

Many proposals for an aluminium alloy to be used as a core material inbrazing sheet have been made. Generally, in the prior art, the alloy isused as a core layer in a brazing sheet with a clad layer on at leastone face. The clad layer provides corrosion protection.

WO 94/22633 describes such an alloy, having the composition in wt. %:

Mn 0.7-1.5 Cu 0.5-1.0, preferabiy >0.6-0.9 Fe 0.4 max. Si 0.15 max. Mg≦0.8 V and/or Cr ≦0.3, preferably ≦0.2 Ti ≦0.1 balance Al andimpurities.

This is used as core material with corrosion-resistant clad layerscontaining Si. The high Cu content is to improve post-brazing sagresistance. Ti is preferably not deliberately added, though is typicallypresent from source material. Preferably Zr is not deliberately added.Cr and/or V are said not to improve post-brazing corrosion resistance,but contribute to post-brazing strength and sag resistance.

U.S. Pat. No. 4,761,267 describes a core alloy for brazing, which hasimproved secular corrosion resistance due to a sacrificial anode or afiller metal on the water-contacting side. Thus the core alloy is usedwith clads on both sides. The composition is in wt. %:

Mn 0.6-1.0 Cu 0.5-1.0 Fe 0.3 max. Si 0.1 max. Mg optionally 0.05-0.4 Ti0.1-0.3 Cr optionally 0.05-0.4 Zr optionally 0.05-0.4 balance Al andimpurities.

Cu is present to allow the filler metal and sacrificial anode todemonstrate the sacrificial anode effect. It also increases strength. Cuis said to decrease the corrosion resistance of the core alloy itself.Mg, Cr and Zr are optional elements for increasing strength. In none ofthe examples are Mg and Cr both present, and in only one are Cr and Zrpresent.

Another approach to obtaining corrosion resistance in core alloys isshown in EP-A-492796, where the core alloy contains in wt. % either

Mn 0.5-1.5

at least one of: Ti (0.05-0.3) and

Zr (0.05-0.4)

or

Mg 0.05-1.0

Si 0.05-0.3, preferably 0.1-0.2

at least one of: Ti (0.05-0.3) and

Zr (0.05-0.4).

Also optional in either case are Fe (0.03-1.0) and Cu (0.05 to 0.2). Inparticular, Si is said to increase strength and is therefore preferablyat 0.1-0.2. Cu at above 0.2 is said to be disadvantageous. Cr is notused. This core alloy is provided with clad layers.

JP-A-4-297541 discloses a core alloy for brazing tube, of composition:

Mn 0.3-1.5 Cu 0.2-0.9 Mg 0.2-0.5 Si 0.1-0.3 Fe 0.1-0.7 Ti 0.1-0.3optionally either or both of: Zr (0.05-0.2) Gr (0.05-0.2) balance Al andimpurities.

This core alloy is assembled into tube with clad layers. Cu is forstrength and to give corrosion resistance with the clad layers. Si isused for strength improvement, but at less than 0.1% has insufficienteffect. Zr and Cr are for strength improvement, and in the exampleswhere they are employed Cu is 0.5%.

JP-A-63-186847 discloses a core alloy for brazing material used with asacrificial anode clad layer on one face. The composition is, in wt. %:

Mn 1.0-1.5 Cu 0.3-0.6 Mg 0.1-0.5 Cr 0.05-0.35 Zr 0.05-0.35 optionally,one or both of V (0.05-0.35) Ti (0.05-0.35) Fe 0.5 max. Si 0.5 max.

Cr and Zr increase strength, and in the examples given total at least0.3 wt. %. Si is an impurity, present at 0.15 wt. % in examples, andreducing corrosion resistance above 0.5 wt. %.

Corrosion resistance is of high importance especially in brazing sheetfor use in automobile radiators. Long-life alloys are those which in theSWAAT test without perforations according to ASTM G-85 exceed 10-12 days(see K. Scholin et al., VTMS 1993, SAE P-263).

SUMMARY OF THE INVENTION

The object of the present invention is to provide a core alloy forbrazing sheet which has improved properties over the alloys of the priorart, and in particular provides a combination of high post-brazingstrength and high corrosion resistance. It is a particular feature thatthe core alloy of the invention does not require post-brazing ageingtreatment, and that the core alloy has high corrosion resistance in theabsence of the sacrificial anode coating layer which is generallyemployed in the prior art.

According to the invention, there is provided an aluminium alloy for useas a core material in brazing sheet, consisting of, in weight %:

Mn 0.7-1.5 Cu 0.6-1.0 Fe not more than 0.4 Si less than 0.1 Mg 0.05-0.8Ti 0.02-0.3 Cr 0.1-0.25 Zr 0.1-0.2 balance Al and unavoidable impurities

wherein 0.20≦(Cr+Zr)≦0.4, the alloy being capable of obtaining in thepost-brazing state 0.2% yield strength of at least 65 MPa and having acorrosion life of more than 11 days in a SWAAT test without perforationsin accordance with ASTM G-85.

This aluminium alloy has good mechanical properties and a good corrosionresistance of over 11 days in the SWAAT test without perforationsaccording to ASTM G-85. In the best examples, this corrosion resistanceis more than 16 days. This level of corrosion resistance qualifies thealloy as a long-life product. The alloy is a non-heat-treatable alloy.It is believed that the excellent properties are the result of thespecific combination of the contents of particularly Cu, Si, Ti, Cr andZr, which are all within relatively narrow ranges. Notably, the alloyhas a high corrosion resistance in a brazing sheet without the presenceof a clad layer acting as a sacrificial anode on the side contactingaqueous cooling fluid in use.

The aluminium alloy is of the AA3xxx type, Mn being the main alloyingelement in order to obtain the desired corrosion resistance. At least0.7% is required for obtaining the desired corrosion resistance, whilean Mn content of over 1.5% does not produce any significant improvementsin respect of the strength because coarse Al—Mn-containing compounds areformed. A further disadvantage of coarse Al—Mn-containing compounds isthat they reduce the rollability of the aluminium alloy. More preferablythe Mn content is in a range of 0.8-1.2%.

Fe is present in all known aluminium alloys but in the aluminium alloysin accordance with the invention it is not a required alloying elementand is not deliberately added. With a high Fe content among other thingsthe corrosion resistance decreases. The admissible Fe content is 0.4%maximum and preferably 0.2% maximum.

The admissible Si content is 0.1% maximum. This low Si content iscritical for the excellent long-life corrosion performance of the corealloy, because the low Si content promotes the formation of asacrificial precipitation layer at the original filler-core interfaceduring the brazing cycle. The filler in this case is a Si-containing lowmelting brazing alloy of conventional type. If the precipitate bandknown as ‘brown band’ is not present then in SWAAT testing the corrosionproceeds in an accelerated intergranular manner. When a precipitate bandis present, the sacrificial nature of the band deflects the corrosion ina lateral manner, i.e. along the direction of the band parallel to theoriginal filler-core interface, preventing through thicknesspenetration.

In the alloy with Si <0.1%, during brazing Si diffuses from the fillerinto the core. It appears that increasing the Si content reduces thesolid solubility of Mn in aluminium, and hence the precipitation of Mncontaining precipitates, i.e. α-MnSiAl, is enhanced. This favouredprecipitation results in a dense band of precipitates, typically 40 to70 μm thick in this region. For an effective precipitate band to formthere has to be sufficient Mn available for combination with the Si. itappears therefore critical to keep Si (and preferably Fe) levels verylow to prevent the formation of stable compounds during hot rolling andannealing which decrease the effective Mn level for the formation of thelocalized band. With a silicon content of over 0.1% in the alloy the Sireacts with Mn to form the α-AlMnSi phase in increasing quantities priorto brazing to the detriment of corrosion performance. As the Si contentis increased the width of the precipitate band decreases, decreasingcorrosion performance. At levels above 0.10% long-life performance isusually not achieved. It is the combination of these diffusiongradients, the higher concentration of Mn and Cu in solid solutionmaking the core more noble to corrosion, and the presence of localizedgalvanic cells in the sacrificial band, that are responsible for thesacrificial protection. In the core alloy in accordance with thisinvention exhibiting excellent SWAAT resistance the sacrificial layerhad a corrosion potential typically 30 mV lower than the under-layingcore as measured according to ASTM G69.

Mg is added to the aluminium alloy since it is to serve as core alloyand be processed by vacuum brazing. If a flux brazing process isapplied, then the Mg content is preferably lower than 0.4%. The Mgcontent is 0.8% maximum and preferably 0.5% maximum.

Cu increases the strength of the aluminium alloy. With a Cu content ofover 1.0% undesired coarse Cu-containing compounds can be formed. It hasbeen found that with a Cu content in a range of 0.6-1.0% the strength isoptimum, while the desired long-life corrosion resistance does notdecrease. Preferably the Cu content is more than 0.6%, particularly atleast 0.7%.

The added Cr improves among other things the strength of the aluminiumalloy in the post-brazed condition, particularly in combination with thehigh Cu content. With a Cr content of more than 0.25% there isdecreasing advantage in respect of the increase in strength. Thereforethe Cr maximum is taken at 0.25%. Preferably, the amount of Cr is0.14-0.25%. The Cr content may optionally be substituted partially orwholly by V in the same amount, since V has an equivalent effect.Casting trials have indicated that with increasing Cr concentrationthere is an increased risk of the formation of coarse Cr containingintermetallic compounds. These compounds have been analysed to bepredominantly Cr—Mn rich in composition and the risk of the formation ofthese particles increases with higher Mn levels as well as Cr level.These coarse intermetallics are detrimental to mechanical properties asthey decrease the effective Mn and Cr for strength purposes, and arealso detrimental for formability and corrosion.

Zr has a significant influence on strength, with increasing Zr improvingthe post-brazed properties. An important factor is that the effect ofthe Zr and the Cr on mechanical properties are additive as clearly shownin FIG. 1 described below, so increased strength benefits can be gainedwith a combined Zr and Cr addition compared to a Cr addition alone.

The significant benefit of Zr additions is therefore that highermechanical properties can be gained with combined Zr+Cr (and Ti) withoutthe risk of formation of detrimental coarse intermetallics than with Cralone. Casting conditions (temperature, solidification rates, etc) canbe tailored to maximize the allowable total additions of Zr, Cr (and Ti)to maximize strength. The strength and performance of the material cantherefore be optimized in this manner.

Zr additions also have additional benefits in that Zr increases therecrystallization temperature of the material, increases the sagresistance, and also promotes the formation of elongated ‘pancake’grains after brazing. These elongated pancake grains contribute to thegood corrosion performance of the material by increasing the lateraltendency of the corrosion attack in a similar manner to the role of thesacrificial layer described above. Zr is restricted to a maximumaddition level of 0.2%, since above this level problems can beencountered in casting due to incomplete dissolution.

It has also been found that Ti additions are also effective inincreasing strength, particularly in conjunction with Zr. The Ti levelis therefore specified in the range 0.02 to 0.3%, preferably 0.05 to0.3%, more preferably 0.08 to 0.2%.

The optimized combined additions of Cr, Zr and Ti in terms of mechanicalproperties have been found not to significantly affect corrosion.

The Ti content, which possibly cooperates with small amounts of Bpresent, is higher than is strictly necessary for obtaining grainrefining of the casting structure. Ti is deliberately added, in theinvention, to the desired level.

In the invention it is of importance to maintain the desired ratio of Crand Zr. As well as the narrow ranges of Cr and Zr, the total of Cr andZr is limited to 0.2-0.4%, preferably 0.25-0.35%.

By unavoidable impurities is meant as is normal that any additionalelement is less than 0.05% and the total of such elements is less than0.15%.

In order to further improve the corrosion resistance of a brazing sheetproduct comprising the aluminium alloy in accordance with the inventionas core alloy, it is possible to add Zn to the alloy in a range of up to1.5% maximum.

Preferably in the aluminium alloy in accordance with the invention thetotal of Zr and Ti is not more than 0.3%.

In the aluminium alloy in accordance with the invention, in which the Cucontent is in a range of 0.6-1.0%, copper is found to be present in thesolid solution and in the τ-phase, Al₂₀Mn₃Cu₂, both before and afterbrazing. The size of these τ-phase particles is in the range 50-250 nm.Although τ-phase is present after brazing, sufficient Cu is retained insolid solution for the desired increase in post-brazed properties.

The strength in the post-brazing state can be measured by conducting asimulated brazing cycle, as is conventional in the art. Since the corealone provides the tensile strength of the brazing sheet, this cycle maybe carried out on the core alloy alone or on a sheet having core andclad layers. The simulated brazing cycle used here is heating in afurnace and holding at 605-610° C. for 5 minutes, followed by aircooling.

The invention also consists in brazing sheet comprising, as corematerial (i.e. strength providing material), the alloy of the inventiondescribed above. While as mentioned a clad or coating layer acting as asacrificial anode in contact with water is not required, such a layermay be provided on one or both sides of the core alloy. On one side, incontact with the core alloy, there will normally be a clad layer in theform of a conventional low melting alloy filler layer.

The invention further consists in use of the aluminium alloy of theinvention described above as core material of a brazing sheet in abrazed assembly. In such an assembly, the aluminium alloy core materialmay be directly in contact with the brazing alloy which is melted at thebrazing temperature. Because the aluminium alloy of the invention isnon-heat-treatable, i.e. does not depend for its tensile strength on apost-brazing ageing treatment, such a treatment need not be performed inuse of the present alloy in a brazed assembly.

The invention also provides a brazed assembly comprising at least twomembers bonded together by means of a brazing alloy, at least one of themembers being of sheet material comprising the aluminium alloy of theinvention described above as its core.

Brazing sheet with good long-life properties and with the aluminiumalloy in accordance with the invention as core alloy, may be made by amethod which comprises the steps:

(a) casting an ingot of the core alloy;

(b) providing the core alloy with a clad layer on at least one side;

(c) hot-rolling;

(d) cold-rolling to the desired finished thickness.

In this context casting an ingot of the core alloy is taken to mean thatmolten aluminium is solidified with the aid of casting techniques whichare existing or being developed, such as DC-(semi)-continuous casting,EMC casting, continuous casting, EMS casting, block casting, etc.

After casting, the ingot of the core alloy obtained is milled andprovided on at least one side with a clad layer of the desiredcomposition. The combination obtained of milled ingot and a clad layeris then heated to within a range of 375-550° C. and preferably held inthat temperature range as briefly as possible in order to keep the corealloy as much as possible in solid solution, or so that smallMn-containing precipitates form which are small enough to disappearagain at a temperature of about 600° C. in a brazing cycle carried outsubsequently. Then the combination is hot-rolled so as to obtain a goodbond between the core alloy and the clad layer and the sheet thicknessof the combination is reduced to within a range of 1-10 mm in ordersubsequently to b e cold-rolled to any desired finished thickness.

It is preferred in this method the cast ingot is homogenized prior tostage by at least a heat treatment of ½-24 hours at a temperature higherthan 550° C., and preferably lower than 625° C. This achieves the effectof improving the formability of the aluminium alloy during rolling. Withgood process management of the homogenization cycle this does notnecessarily mean that the corrosion resistance of the finished productdecreases.

Preferably during stage (d) the brazing sheet undergoes an intermediateheat treatment (inter-annealing) during cold-rolling. With anintermediate heat treatment during the cold-rolling, wherein the heattreatment is carried out in a favorably selected temperature and timerange, this does not necessarily mean that the corrosion resistance ofthe finished brazing sheet is negatively affected. In order to obtain anadequate degree of work hardening in the brazing sheet, the thickness ofthe brazing sheet is reduced by preferably at least 50% following theintermediate heat treatment in one or more cold-rolling stages.

Prior to carrying out a brazing cycle it is usual for the combination tobe converted into a desired shape. Cold-rolled sheet does not haveoptimum formability so that it is often necessary to anneal the sheet orcombination in order to obtain the desired formability. For fullannealing this is usually carried out in a temperature range of 350-425°C., and for partial annealing this is usually carried out in atemperature range of 250-350° C.

When the brazing sheet product with the aluminium alloy in accordancewith the invention as core alloy, is provided with one or more fillerlayers, these may comprise an aluminium alloy with an Si content in arange of 5-15 wt. %. Alternatively the clad layer is an aluminium alloywith Zn as main alloying element. The advantage of such a brazing sheetproduct is that it may be processed with existing processing techniquessuch as vacuum brazing and controlled atmosphere brazing such as fluxbrazing.

The aluminium alloy in accordance with the invention or a brazing sheetproduct with the aluminium alloy in accordance with the invention ascore layer is perfectly suitable for being processed to any desiredsheet thickness and to any desired temper. Furthermore, it is possibleby means of extrusion techniques to process the aluminium alloy into(semi) finished products with a good corrosion resistance.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 of the accompanying drawing is a graph showing the effect of theCr and Zr contents on 0.2% yield (proof) strength.

EXAMPLES

The aluminium alloy and brazing sheet in accordance with the inventionwill now be illustrated by non-limitative examples.

Example 1

The following test was carried out on a laboratory scale. Ingots oftwelve aluminium alloys for use as core alloys in brazing sheets werecast and solidified at a cooling rate comparable to those cooling ratesthat occur in DC-casting. Table 1 gives the compositions of the alloys,in % by weight (balance Al and impurities). The ingots were heated to450° C., hot-rolled to a thickness of 5 mm, and then cold-rolled to afinished thickness of 0.35 mm. The cold-rolled sheets were annealed for3 hours at a temperature of 350° C. Mechanical properties were assessedand these are given in Table 2. The aluminium alloys were tested in the“post-brazing state”, i.e. after the simulated brazing cycle givenabove.

Alloys 1 and 6 are reference alloys which come within the compositionalrange of the aluminium alloys of WO 94/22633 discussed above. Aluminiumalloys 2-5 and 7-9 are alloys in accordance with the invention. Theothers are for comparison purposes.

From the results given in Table 2 it can be seen that the aluminiumalloy in accordance with the invention has a higher yield strength andtensile strength than the known aluminium alloy of WO 94/22633.

Comparison of alloys 7 and 8 shows that a higher Cu content results in ahigher strength. Comparison of alloys 4 and 5 shows that an increase ofonly the Ti content results in a small increase in the strength.

The results further show that in a high Zr content in combination with ahigh Ti content results surprisingly in an alloy with a high strength, aconcept not found in WO 94/22633.

TABLE 1 Alloy Fe Si Mn Cu Mg Ti Cr Zr (Cr + Zr) (Ti + Zr) 1 0.18 0.070.75 0.93 0.36 0.09 0.02 — 0.02 0.09 2 0.18 0.08 0.74 0.93 0.36 0.090.15 0.11 0.26 0.20 3 0.17 0.06 1.06 0.93 0.36 0.09 0.15 0.12 0.27 0.214 0.19 0.06 1.08 0.92 0.34 0.15 0.16 0.11 0.27 0.26 5 0.17 0.07 1.150.94 0.36 0.07 0.15 0.11 0.26 0.18 6 0.18 0.07 0.76 0.60 0.23 0.09 0.02— 0.02 0.09 7 0.18 0.07 1.09 0.98 0.49 0.02 0.15 0.11 0.26 0.13 8 0.170.06 1.09 0.60 0.48 0.02 0.16 0.10 0.26 0.12 9 0.17 0.06 1.05 0.92 0.460.14 0.15 0.10 0.25 0.24 10 0.19 0.08 1.22 0.94 0.48 0.02 0.15 0.11 0.260.13 11 0.17 0.07 1.09 0.35 0.51 0.01 0.02 — 0.02 0.01 12 0.19 0.08 1.100.75 0.50 0.02 0.15 0.08 0.23 0.10

TABLE 2 0.2% yield tensile elongation at Alloy strength [MPa] strength[MPa] fracture [%] 1 63 176 18.7 2 67 176 18.9 3 69 184 17.2 4 72 16615.1 5 74 190 19.5 6 54 157 21.3 7 75 194 17.3 8 69 177 15.8 9 78 19616.6 10 77 199 17.2 11 60 165 18.8 12 67 17S 12.4

Alloys 1, 3, 4 and 5 of Table 1, and three alloys (nos. 13-15) notincluding Ti, Cr and Zr were subjected to the SWAAT test withoutperforation according to ASTM G-85. The compositions of these alloysincluding those of alloys 1, 3, 4 and 5 for convenience, and the SWAATtest results are given in Table 3 (% by weight, balance Al andimpurities). The SWAAT results for alloys 13, 14 and 15 show thedetrimental effect on corrosion resistance of increasing Si above 0.1%to 0.32%.

TABLE 3 SWAAT Alloy Fe Si Mn Cu Mg Ti Cr Zr (Days) 1 0.18 0.07 0.75 0.930.36 0.09 0.02 — 11 3 0.17 0.06 1.06 0.93 0.36 0.09 0.15 0.12 21 4 0.190.06 1.08 0.92 0.34 0.15 0.16 0.11 16 5 0.17 0.07 1.15 0.94 0.36 0.070.15 0.11 20 13 0.10 0.09 1.06 0.67 0.34 — — — >20 14 0.10 0.20 1.060.93 0.57 — — — 7 15 0.10 0.32 1.07 0.66 0.33 — — — 7

Example 2

Alloys having the base composition, in wt. %:

Mn 1.1 Cu 0.9 Mg 0.5 Si 0.09 Fe 0.17 Ti 0.08 balance Al and impurities.

and containing varying amounts of Cr and Zr were made, and the 0.20%yield (proof) strength in post-brazing condition (simulated brazingcycle) was measured. The results are plotted in FIG. 1. Cr and Zr bothenhance strength, and it can be seen that in the region of 0.20% Cr, theeffect of addition of 0.1-0.2% Zr is more significant.

What is claimed is:
 1. A brazing sheet comprising an aluminium alloy foruse as a core material in the brazing sheet, the core material having ahigh corrosion resistance in the absence of a sacrificial anode coatinglayer, comprising, in weight %: Mn 0.7-1.5 Cu 0.6-1.0 Fe not more than0.4 Si at most 0.08 Mg 0.05-0.8 Ti 0.02-0.09 Cr 0.1-0.25 Zr 0.1-0.2

wherein 0.20<(Cr+Zr)≦0.4, wherein the core has no coating layer foracting as a sacrificial anode in contact with water, the alloy beingcapable of obtaining in the post-brazing state 0.2% yield strength of atleast 65 MPa and having a corrosion life of more than 11 days in a SWAATtest without perforations in accordance with ASTM G-85.
 2. A brazingsheet according to claim 1, wherein the corrosion life in said SWAATtest is at least 16 days.
 3. A brazing sheet according to claim 1,wherein the Cu content is 0.7-1.0 wt. %.
 4. A brazing sheet according toclaim 1, wherein the Ti content is 0.08-0.09 wt. %.
 5. A brazing sheetaccording to claim 1, wherein the Mn content is 0.8-1.2 wt. %.
 6. Abrazing sheet according to claim 1, wherein said core material has aclad layer on at least one side thereof.
 7. A method of making a brazingsheet according to claim 1, comprising providing said alloy as corematerial of the brazing sheet in a brazed assembly, applying a cladlayer to the core material.
 8. A method of use according to claim 7,wherein the core material contacts at least one said clad layer of a lowmelting point brazing alloy.
 9. A brazed assembly comprising at leasttwo members bonded together by means of a brazing alloy, at least one ofsaid members being of sheet material comprising a brazing sheetaccording to claim
 1. 10. A brazing sheet comprising an aluminium alloyfor use as a core material in the brazing sheet, the core materialhaving a high corrosion resistance in the absence of a sacrificial anodecoating layer, consisting of, in weight %: Mn 0.7-1.5 Cu 0.6-1.0 Fe notmore than 0.4 Si at most 0.08 Mg 0.05-0.8 Ti 0.02-0.09 Cr 0.1-0.25 Zr0.1-0.2 balance Al and unavoidable impurities

wherein 0.20<(Cr+Zr)≦0.4, wherein the core has no coating layer actingas a sacrificial anode in contact with water, the alloy being capable ofobtaining in the post-brazing state 0.2% yield strength of at least 65MPa and having a corrosion life of more than 11 days in a SWAAT testwithout perforations in accordance with ASTM G-85.